1. Field of the Invention
The present invention relates to a probe apparatus for use in examining an object such as a semiconductor wafer, and a method of alignment for the probe apparatus.
2. Description of the Related Art
A number of chips are formed on a surface of an object such as a semiconductor wafer. The chips are regularly arranged at predetermined intervals. A number of pads are formed at predetermined locations on each chip. The pads are connected to various semiconductor elements provided within the chip. The electric characteristics of the chip are examined with probe needles of an examining apparatus put in contact with the corresponding pads within the chip. A defective chip is discriminated by marking or other means. Normally, a probe apparatus is used for this kind of examination for the purpose of automation.
The newest type of the probe apparatus has a vertically movable chuck for holding a semiconductor wafer or an object to be examined. The chuck is supported on a stage and is movable in a horizontal plane.
A stationary camera is provided on the alignment bridge of the probe apparatus. The stationary camera is used to detect the position of a given chip on the surface of the semiconductor wafer held by the chuck. On the other hand, a movable camera is provided on the stage so as to be vertically movable. The movable camera is used to detect the position of the probe needle put in contact with a predetermined location on the chip.
According to the above conventional apparatus, alignment between the chip and probe needles is performed, on the premise that the positional relationship (i.e. distance) between the chip to be detected by the stationary camera and the movable camera for detecting the probe needles is constant. However, when examination is performed at high temperatures or low temperatures, the positional relationship slightly varies owing to thermal expansion or contraction of the semiconductor wafer or chuck, or a variation in the position of the wafer on the chuck. Consequently, in the above conventional apparatus, precision of the alignment lowers owing to the variation in the positional relationship.